109 research outputs found
Method for comparing finite temperature field theory results with lattice data
The values of the presently available truncated perturbative expressions for
the pressure of the quark-gluon plasma at finite temperatures and finite
chemical potential are trustworthy only at very large energies. When used down
to temperatures close to the critical one Tc, they suffer from large
uncertainties due to the renormalization scale freedom. In order to reduce
these uncertainties, we perform resummations of the pressure by applying
Pade-related approximants to the available perturbation series for the
short-distance and for the long-distance contributions. In the two
contributions, we use two different renormalization scales which reflect
different energy regions contributing to the different parts. Application of
the obtained expressions at low temperatures is made possible by replacing the
usual four-loop barMS beta function for alpha_s by its Borel-Pade resummation,
eliminating thus the unphysical Landau singularities of alpha_s. The obtained
results are remarkably insensitive to the chosen renormalization scale and can
be compared with lattice results -- for the pressure (p), the chemical
potential contribution (delta p) to the pressure, and various susceptibilities.
A good qualitative agreement with the lattice results is revealed down to
temperatures close to Tc.Comment: 24 pages, 17 figures, revtex4; Ref.[25] is new; the ordering of the
references and grammatic and stylistic errors are corrected - version as it
appears in PR
Gauge Coupling Beta Functions in the Standard Model to Three Loops
In this paper we compute the three-loop corrections to the beta functions of
the three gauge couplings in the Standard Model of particle physics using the
minimal subtraction scheme and taking into account Yukawa and Higgs self
couplings.Comment: 4 pages, 1 figure, v2: minor changes, references adde
Renormalization constants and beta functions for the gauge couplings of the Standard Model to three-loop order
We compute the beta functions for the three gauge couplings of the Standard
Model in the minimal subtraction scheme to three loops. We take into account
contributions from all sectors of the Standard Model. The calculation is
performed using both Lorenz gauge in the unbroken phase of the Standard Model
and background field gauge in the spontaneously broken phase. Furthermore, we
describe in detail the treatment of and present the automated setup
which we use for the calculation of the Feynman diagrams. It starts with the
generation of the Feynman rules and leads to the bare result for the Green's
function of a given process.Comment: 44 pages, 9 figures; v2: sign in eq.(29) corrected; final result
unchange
Off-shell two loop QCD vertices
We calculate the triple gluon, ghost-gluon and quark-gluon vertex functions
at two loops in the MSbar scheme in the chiral limit for an arbitrary linear
covariant gauge when the external legs are all off-shell.Comment: 29 latex pages, 32 figures, anc directory contains txt file with
electronic version of vertex functions for each of the three 3-point cases in
the MSbar scheme and includes the projection matrice
Duality between constraints and gauge conditions
It is shown that in the first order gauge theories under some general
assumptions gauge conditions can play the role of new local symmetry
generators, while the original constraints become gauge fixing terms. It is
possible to associate with this new symmetry a second BRST charge and its
anticommutator with the original BRST charge is the Hodge operator of the
corresponding cohomology complex.Comment: 7 pages, LaTeX, some changes in the BRST sectio
Two loop QCD vertices at the symmetric point
We compute the triple gluon, quark-gluon and ghost-gluon vertices of QCD at
the symmetric subtraction point at two loops in the MSbar scheme. In addition
we renormalize each of the three vertices in their respective momentum
subtraction schemes, MOMggg, MOMq and MOMh. The conversion functions of all the
wave functions, coupling constant and gauge parameter renormalization constants
of each of the schemes relative to MSbar are determined analytically. These are
then used to derive the three loop anomalous dimensions of the gluon, quark,
Faddeev-Popov ghost and gauge parameter as well as the beta-function in an
arbitrary linear covariant gauge for each MOM scheme. There is good agreement
of the latter with earlier Landau gauge numerical estimates of Chetyrkin and
Seidensticker.Comment: 36 latex pages, anc directory contains txt file with anomalous
dimensions, beta-functions, coupling constant mappings, conversion functions
and amplitudes in analytic for
Do we need Feynman diagrams for higher orders perturbation theory?
We compute the two and three loop corrections to the beta function for
Yang-Mills theories in the background gauge field method and using the
background gauge field as the only source. The calculations are based on the
separation of the one loop effective potential into zero and positive modes and
are entirely analytical. No two or three loop Feynman diagrams are considered
in the process.Comment: version published in Phys. Lett.
Quantum properties of a non-Abelian gauge invariant action with a mass parameter
We continue the study of a local, gauge invariant Yang-Mills action
containing a mass parameter, which we constructed in a previous paper starting
from the nonlocal gauge invariant mass dimension two operator F_{\mu\nu}
(D^2)^{-1} F_{\mu\nu}. We return briefly to the renormalizability of the model,
which can be proven to all orders of perturbation theory by embedding it in a
more general model with a larger symmetry content. We point out the existence
of a nilpotent BRST symmetry. Although our action contains extra
(anti)commuting tensor fields and coupling constants, we prove that our model
in the limit of vanishing mass is equivalent with ordinary massless Yang-Mills
theories. The full theory is renormalized explicitly at two loops in the MSbar
scheme and all the renormalization group functions are presented. We end with
some comments on the potential relevance of this gauge model for the issue of a
dynamical gluon mass generation.Comment: 17 pages. v2: version accepted for publication in Phys.Rev.
Hamiltonian Approach to Supergravity
We study supergravity in a covariant and gauge independent way. The
theory is obtained from bosonic gravity following the square root method
and the diffeomorphism superalgebra is explicitly computed. We argue that our
approach could be a procedure for introducing nontrivial physics in quantum
(super)gravity.Comment: 11pp, Plain tex, IPNO-TH 92/7
Abelian Subset of Second Class Constraints
We show that after mapping each element of a set of second class constraints
to the surface of the other ones, half of them form a subset of abelian first
class constraints. The explicit form of the map is obtained considering the
most general Poisson structure. We also introduce a proper redefinition of
second class constraints that makes their algebra symplectic.Comment: to appear in Phys. Lett.
- …